Various types of protective covers for electrical outlets have been described in patent litterature.
For example, U.S. Pat. No. 4,605,270 issued Aug. 12, 1986 to Aslizadeh describes a protective cover for an electrical outlet that comprises a pair of slideable closure plates and a pair of coil spring-actuated blocking plates wherein both plates are positioned within the boundaries of the rectangular openings in the front wall of the cover.
Also, U.S. Pat. No. 3,068,442 issued Dec. 11, 1962 to Kubik et al. describes a safety guard of the type described which comprises a box-like enclosure dimensioned to fit over the face plate of a wall socket having a pair of vertically aligned sockets and a slide member mounted for sliding vertical movement within the enclosure. The safety guard further comprises upper and lower bars which are disposed in overlaying relationship to the socket openings. The slide member is moveable downwardly to move the bars away from the socket openings and bring free areas into alignment with the socket openings. Each bar, upon release of the slide member is held in downward position if a plug is inserted in its socket opening and is free for independant return movement to its normal position by the urging of the springs if no plug is inserted in its opening.
Both of these protective systems provide for spring-actuated blocking plates which are moveable to automatically cover the socket openings if a plug is removed from a socket. However, they are not fully protective in that most children will be able to master the sliding movement of the plates, either accidentally or through observation.